1. Field of the Invention
The present invention relates to a device for melting, storing and feeding a metal material from a bar-shaped metal material intended for an injection apparatus for molding a metal product, in which bar-shaped metal materials such as magnesium and aluminum are melted and injected into a mold.
2. Description of the Related Art
Among conventional injection apparatuses for molding a metal product is one in which a melting furnace is installed on an injection cylinder having a plunger inside (Japanese Patent Application Laid-Open No. 2004-291032). A solid material is melted and stored in the melting furnace, and the plunger is retreated to create a material measuring chamber in the front part of the cylinder, into which the molten material is fed from the melting furnace and measured (accumulated) for a single shot of injection. The plunger is then advanced to inject the measured material into a mold from a nozzle at the top of the cylinder.
In another injection apparatus, the interior of an injection heating cylinder is used as a melt holding chamber (Japanese Patent Application Laid-Open No. 2005-40807). An injection plunger is retreated to create a material measuring chamber in front of the plunger, into which a molten material in the melt holding chamber is accumulated and measured for a single shot of injection. The injection plunger is then advanced to inject the single shot of measured material into a mold from a nozzle at the top of the injection heating cylinder. This injection apparatus has a melting device which includes: an insulated storage barrel erected on the melt holding chamber of the injection heating cylinder; and a melting barrel arranged sideways on the top side area of the insulated storage barrel. The melting barrel melts bar-shaped metal material, and the insulated storage barrel stores the molten metal material for a large number of shots. In yet another injection apparatus, the insulated storage barrel is made of a barrel having a constricted bottom, and a barrel for melting bar-shaped metal materials is erected on the top of the insulated storage barrel (Japanese Patent Application Laid-Open No. 2007-160368).
Take the case of the apparatus where a solid metal material is melted and stored in the melting furnace, and the molten metal material is measured for a single shot each time the plunger is retreated for injection. Here, the solid metal material is immersed and melted in the molten metal material that has been melted and stored in the furnace in advance. The melting is thus quick if there is some molten metal material in the melting furnace. When starting molding without molten metal material, however, the immersion melting will not occur and therefore it takes a long time before the bar shaped metal materials are melted up to an amount capable of immersion melting. In other words, the device for melting and storing a metal material using the melting furnace requires a long time for molding startup, with the problem of accordingly poor efficiency of the molding operation.
When melting a metal material in a melting furnace, the metal material in the furnace drops in temperature, i.e., causes temperature variations each time a new piece of metal material is loaded. The reason for this is that the loaded metal material, even if preheated, has a lower temperature than that of the molten metal material stored in the furnace. In order to avoid this loading-based temperature drop from affecting the molten metal material to be fed to the injection cylinder from the bottom of the melting furnace, the melting furnace must therefore be formed deep for the sake of an increased storage capacity. This inevitably makes the furnace body large in size and heavy in weight, producing the problem that the melting furnace can hardly be adopted for the device for melting and storing a metal material, to be installed on the injection cylinder.
Take the cases where bar-shaped metal materials are loaded into and melted in the melting barrel which has heating means on its periphery. This melting is effected by radiant heat which provides a melting rate lower than by the immersion melting, whereas the entire bar-shaped metal materials can be heated simultaneously from the periphery for high heating efficiency. The molten metal material flowing out of the melting barrel is stored into the insulated storage barrel of the injection heating cylinder or into a heating cylinder having an injection plunger inside, which precludes loading-based temperature variations. In addition, since a smaller amount of molten metal material needs to be stored for molding startup than with the melting furnace, the molding startup time can be reduced with the advantage of earlier start of the molding operation.
In the apparatuses where the molten metal material is stored in the storage unit outside the injection heating cylinder and is measured out for each single shot by retreating the injection plunger, the storage capacity is limited to that of the insulated storage barrel since the injection heating cylinder itself is not available for storing the metal material. The number of melting barrels that can be installed on the insulated storage barrel is also limited to one. Consequently, in terms of the relationship between the melting speed of the metal material and the molding cycles, it is sometimes difficult to melt and feed a sufficient amount of molten metal material corresponding to the molding cycles depending on the weight of metal products to be molded.
The insulated storage barrel may be increased in capacity and in size so as to store a larger amount of a molten metal material. This, however, makes the molten metal material to reside longer in the insulated storage barrel, so that temperature differences can occur easily from molten metal material that is newly supplied from the melting barrel. This is prevented by raising the temperature setting of the insulated storage barrel, which entails the problem of an inevitable increase in the thermal energy consumption.